1. Field of the Invention
The present invention relates to a video camera having an aperture correction circuit.
2. Description of the Prior Art
U.S. Pat. No. 4,855,829, for example, describes an aperture correction circuit that is applied to a video camera. As is well known, the aperture correction circuit is utilized in order to compensate for a deterioration of response of an image pickup device and to emphasize a sharpness in the video camera.
Video cameras having a CCD (charge-coupled device) formed of 400,000 pixels are now commercially available on the market. The above 400,000-pixel CCD is driven at a horizontal drive frequency of 14.3 MHz. In the above video camera, an output signal from the 400,000-pixel CCD is converted into a digital signal serving as a main line signal by an A/D (analog-to-digital) converter. An aperture correction signal is formed from the digital signal thus converted by an aperture signal forming circuit. Then, the aperture signal thus formed and the digital signal serving as the main line signal are added to provide a corrected digital signal. The corrected digital signal is converted by a video signal forming circuit into a digital luminance signal and digital color difference signals or a digital composite video signal.
In the conventional video camera thus constructed, the A/D converter, the aperture signal forming circuit and the video signal forming circuit are all driven by a clock frequency of 14.3 MHz that is the same frequency as a horizontal drive frequency of the 400,000-pixel CCD. In that case, there are obtained 560 television lines as a horizontal limit resolution.
As a horizontal limit resolution for high-definition television receiver, there must be provided about 700 television lines or more. Therefore, in the conventional video camera, in order to increase a horizontal limit resolution, a pixel G is spatially displaced from pixels R and B by 1/2-pixel pitch, whereby the 400,000-pixel CCD and the A/D converter are driven by the clock frequency of 14.3 MHz and other aperture signal forming circuit, the video signal forming circuit, etc., are driven by a clock frequency of 28.6 MHz. According to this arrangement, a horizontal limit resolution can be increased to 900 television lines. However, if the video camera is arranged as described above, an electric power consumption of the circuits, in particular, an electric power consumption of the video signal forming circuit is increased considerably.